class_docstr: A step load shape
  Keyword arguments:
      step_time -- Time between steps
      step_load -- User increase amount at each step
      spawn_rate -- Users to stop/start per second at every step
      time_limit -- Time limit in seconds
code: def tick(self):
      run_time = self.get_run_time()
  
      if run_time > self.time_limit:
          return None
  
      current_step = math.floor(run_time / self.step_time) + 1
      return (current_step * self.step_load, self.spawn_rate)
  
file_path: milvus/tests/benchmark/milvus_benchmark/runners/test.py
imports: import math
  from locust import User, TaskSet, task, constant
  from locust import LoadTestShape
label_desc: Use image node_id 1 for calling the StepLoadShape obj's underlying member method code with example usage: obj.tick() and returns: unknown,  self, None